1. Field of the Invention
The invention is directed to an x-ray diagnostics installation of the type having an operating voltage generator, an x-ray tube, an x-ray image intensifier, a video camera, a video amplifier, an integration circuit and a control circuit that acts on the operating voltage generator for controlling the dose rate. In fluoroscopy mode, such x-ray diagnostics installations serve the purpose of reproducing x-ray images on a monitor.
2. Description of the Prior Art
German OS 31 19 751 discloses an x-ray diagnostics installation of the above type wherein a video pick-up device converts an image visible on the output luminescent screen of an x-ray image intensifier into an electrical signal that, is amplified, digitized by an analog-to-digital converter (A/D converter), and integrated in an image memory. A central control device generates all clock and control signals of the entire x-ray diagnostics installation. The control device effects control of the dose of the x-ray generator on the basis of a measured signal.
It is also known in x-ray diagnostics installations to undertake a gain control of the video pick-up device only when the range of control of the dose rate control is downwardly transgressed. When, however, the automatic gain control of the video amplifier takes effect, this means that only slight light, and thus a small signal are available. A disadvantage is that the signal-to-noise ratio (S/N) is thereby degraded.